Migratory paraffin scraper



Oct. 16, 1962 J. c. TRIPPLEHORN 3,058,524

MIGRATORY PARAFFIN SCRAPER Filed Sept. 14, 1952 31 3i Wi l 2 i3 0 5 V 5d A lliii 4L v f n L i /2 4 i INVENTOR. JAMES C. TRIPPLEHORN SLAP/2MUnited States Patent 3,058,524 MIGRATORY'PARAFFIN SCRAPER James C.Tripplehorn, 1013 Mary Ellen St., Par'npa, Tex. Filed Sept. 14, 1959,Ser. No. 839,888 3 Claims. (Cl. 166-476) This invention relates toparafiin scrapers of the type which is applied loosely to a sucker rodwhile the latter is being reciprocated within a tubing string duringpumping of an oil well, and more particularly the invention relates tomigratory paraffin scrapers which are free to move up and down not onlyvn'th respect to the tubing but also with respect to a length of thesucker rod to which the scraper is applied, the scraper also serving asa rod guide tending to space the rod from the walls of the tubing.

It is a principal object of this invention to provide an improvedparafiin scraper which is free to move axially on the sucker rod whichit surrounds so as to prevent the building up of parafiin deposits onthe sucker rod by scraping the rod itself, the travel of the scraperbeing confined either to that particular rod, or being further confinedto a certain longitudinal portion of the rod by abutments which maycomprise fixed types of rod guides or scrapers which are not free tomove axially of the rod.

It is another primary object of this invention to provide a migratoryparafiin scraper which may be installed on a standard rod havingstandard tool joints without the necessity of severing the rod orotherwise altering it.

It is another major object of this invention to provide a parafiinscraper which is in the form of a G-shaped body having a central boretherethrough adapted to receive and freely pass the sucker rod, theinside diameter of the body being larger than the sucker rod and thebody having a plurality of scraping blades disposed on its outer surfaceat an angle inclined with respect to the axis of the body whichcoincides with the axis of its bore. The blades have outer bearingsurfaces coinciding with the surface of a cylinder coaxial with thebody, and the outside diameter of these bearing surfaces is smaller thanthat of the pump tubing in which the sucker rod and scraper are intendedto operate. The C-shaped body terminates circumferentially in a slotprovided to permit forceable installation of the body on a sucker rod,the slot also assisting the body to present minimum restriction of theoil passage space between the sucker rod and the well tubing. Themeetings of the side surfaces of the blades with the outer bearing.surfaces thereof are purposely made abrupt so that the blades will havescraping edges which are satisfactory for scraping the inner surfaces ofthe well tubing. 1 have also provided a plurality of scraping edgeswithin the bore of the body by including a series of grooves therein,said inner scraping edges cleaning the outside surfaces of the rod. Thepresent parafiin scraper consists of a one-piece molded body integrallyconnected with the scraper blades and of sufiicient axial length that itcannot tilt crosswise in the tubing far enough to become wedged therein.

It is a further very important object of the present invention toprovide a paraflin scraper which is made of a plastic which can bemolded and hardened to retain its shape, and in addition which plastic,at the temperatures encountered in oil wells, is dimensionally stableand Patented Oct. 16, 1962 ice resistant to attack by oil and acids. Theelectrical insulating properties of the plastic are also important sincethey prevent the attack on other adjacent metal parts in the well byelectrolysis. A range of suitable plastics includes the following:

Vinylidene chloride-Rigid compound Polyamides-Molding types, Nylon 1001known as Zytel Polytetra-fluoro ethylene Polychloro-tri fluoro ethylenePolymethyl alpha chloro-acrylate Polyester diallyl phthalate Poly acetalresin The use of plastic in connection with such a scraper is importantfor several reasons. In the first place, manufacturing of such a productcan be conveniently and economically carried out by molding or by someother plastic handling process in order to produce the desired form. Inaddition to obvious advantages which the plastic has over metals,plastics found in the above range also exhibit spring-like qualitiesgenerally thought of in connection with metals, which spring-likequalities permit the scraper to fiex open when being installed on asucker rod without damage or breakage. Another advantage in the use ofthe above plastics results from the fact that the very substance to bescraped by the scraper, namely the paraffin, has very little tendency toadhere to the plastic scraper since paraffin does not tend to ad here tothe smooth non-porous surface. Therefore, the build-up which occurs onmetal paraffin scrapers is substantially absent when the above plasticsare substituted for the metals, and this fact is especially important inconnection with the scraping grooves in the bore of the present scraper,which grooves would become filled and clogged with paraffin if thescraper were made of a material to which paraffin adheres.

Another benefit which results from the use of plastics comes aboutbecause of the fact that the specific gravity of the above plastics isvery similar to the specific gravity of the liquids found in oil wells,and not nearly as different as the specific gravity of most spring-likemetals would be. This feature is of considerable importance because ofthe fact that the paraflin scraper when made of a material having aspecific gravity approximating that of the oil liquids will migratethrough considerable distances during reciprocation of the sucker rodwithin the well tubing. For example, in the case where the stroke of thesucker rod in the tubing is 3 feet, a relatively short scraper, perhapsonly a few inches or so long, will clean a 10- or l5-foot verticallength of sucker rod and tubing despite the relatively short stroke ofthe pump.

Because of the fact that the specific gravity of the scraper is nearlythe same as that of the well liquids, the scraper will Work its wayalong the tubing from one abutment to the next adjacent abutment eventhough this distance may be many times the length of the pump stroke andmany times the length of the scraper. The scraper, of course, does notpass over such a length of sucker rod in one or two strokes, but mayrequire a considerable time to cover the greater length. Tests haveshown, however, that it does periodically cover such a length and thatsuch coverage tends to be repeated at regular enough intervals that themigratory scraper will satisfactorily prevent the building up ofparaffin deposits on both the rod and the tubing. It is well known thatthe Well fluids are 3 not homogeneous but contain oil and water, more orless solid objects, lumps of paraffin, and gas pockets. Thisnon-homogeneous character of the fluid which is being pumped upwardlypartially accounts for the fact that the scraper is caused to migrateover a greater length of rod and tubing than the length of the pumpstroke.

When the present migratory scrapers are employed in combination withfixed scrapers as disclosed in my copending application relating toParafiln Scraper Cornbination, Serial Number 672,268, filed July 16,1957, now Patent 2,997,106, when the sucker rod is descending the columnof fluid is standing substantially still in the vertical direction butit may be caused to rotate by the downward passage of helical blades ofscrapers fixed on the sucker rod. Since the migratory scrapers haveinclined blades on their outer surfaces, and since these scrapers areinitially not rotating with the well fluids but have rotational inertia,they are forced to travel in an axial direction by their screw action inthe column of liquid as the column rotates faster and faster during thedown-stroke of the rod. However, during the up-stroke of the pump rodthis screw action forces the scrapers to travel in the opposite axialdirection in the rotationally decelerating fluid. The relative rates ofrotation in the two directions between the fluids and the migratoryscrapers are varied by collisions between the scrapers and theabove-mentioned solid objects, lumps of parafiin, and gas pockets.Although during the up-stroke of the pump the migratory scrapers arecarried upwardly by the fluid flow, and perhaps by abutment against thenext lower fixed scraper, the migratory scrapers also tend to sinkduring down-strokes of the rod and may also be forced downwardly byabutment against the next higher fixed scraper. Also they drop rapidlythrough gas pockets in the fluid column. It is only when the migratoryscrapers are relatively lighter than the usual steel scrapers that theabove migratory forces all play significant roles in providing migration of the scrapers over a length of rod greater than the length ofthe stroke.

A further object of the invention is to provide a paraffin scraper whichas it is reciprocated performs rotational motion which tends to reservein direction as the direction of reciprocation of the rod in the tubingis reversed. This rotational-reciprocating action exhibits excellentscraping characteristics.

It is another object of the present invention to provide a flattenedsurface at each end of the scraper, which surface lies in a planedisposed normal to the axis thereof, and serves as a land for contactingthe abutments which confine the ambulatory scraper to a certain portionof the sucker rod.

Other objects and advantages of the present invention will becomeapparent in the following discussion of the drawing, wherein:

FIG. 1 is an elevation view of a migratory paraifin scraper according tothe present invention applied to a sucker rod which reciprocates withinpump tubing, the tubing being shown cut away so as to render the scrapervisible;

FIG. 2 is a perspective view of the scraper shown in FIG. 1;-

FIG. 3 is a cross-section taken along line 3-3 of FIG. 1 and showing thescraper in plan view;

FIG. 4 is an elevation view smiliar to the view of the scraper shown inFIG. 3 but showing the scraper rotated about its axis to a difierentposition;

FIG. 5' is a cross-section taken along line S5 of FIG. 4.

Referring to the drawing, FIG. 1 illustrates a length of sucker rod Rpassing through a length of tubing T in which it reciprocates. Aroundthe rod R and within the tubing T is disposed a migratory paralfinscraper -1 according to the present invention and shown in a suspendedposition with respect to the tubing and sucker rod. The scraper 1 asillustrated in the drawing includes a 0-shaped 4 body 2 having an outersurface of generally cylindrical form and having transverse end surfaces2a connected with the outer cylindrical surface by charnfered surfaces2b.

The scraper 1 has a longitudinally disposed central bore 3 therethrough,the bore 3 being of greater diameter than the sucker rod R as can beseen in FIGURE 3. The bore is also provided with a series oflongitudinally disposed grooves 3a in its wall, which grooves areintended to provide abrupt scraping edges along the lines where theymeet the surface of the bore 3.

The body 2 of the scraper is further provided with a slot 20 through itswall and communicating into the bore 3 so as to permit mounting of thebody on a sucker rod R. As can be seen in "FIG. 3, the width of the slot20 is slightly less than the diameter of the sucker rod so that acertain amount of force is required to place the scraper body 2 on asucker rod.

The scraper 1 further includes a plurality of scraper blades 4 whichform an integral part of the scraper and which have side surfaces 4awhich are joined substantially at right angles to the outer cylindricalsurface of the body 2. The scraper blades also include outer bearingsurfaces 4b adapted to bear against the inner surface of the tube T.These outer bearing surfaces 4b coincide with a cylinder which iscoaxial with the axis of the scraper and its bore. The scraper blades 4have tapered ends 4'0 which blend smoothly into the chamfered surfaces2b of the body 2. The blades 4 are further streamlined by longitudinallydisposed surfaces t-d near their ends which narrow the end area of eachblade 4 so that it will present less impedance to the flow of oil pastthe scraper, thus both ends of each scraper blade are effec tivelytapered down to a very small end area so as to reduce to a minimum theimpedance to oil flow thercpast.

The blades 4 are provided at an inclined angle with respect to thelongitudinal axis of the scraper 1 and are of substantially helicalform. The disposition of the blades at an inclined angle causes thescraper to rotate rapidly by virtue of the screw action of the blades inthe well fluids passing the scraper.

The side surfaces 4a of each blade meet the outer hearing surfaces 4bthereof at right angles or at an acute angle so as to provide abrupt andrelatively sharp scraping edges. Likewise the grooves 3a meet thesurface of the bore 3 at substantially right angles so as to form abruptor relatively sharp inner scraping edges to assist the scraper incleaning the rod R during rotation of the scraper thereabout.

It is, of course, to be understood that during pumping of a well thesucker rod R tends to lash back and forth transversely within the tubingT and that therefore the tubing and rod will be in frequent althoughprobably intermittent contact with the inner and outer scraping edges ofthe present migratory paraflin scraper.

The present invention is not to be limited to the exact form shown inthe drawing for obviously changes may be made therein within the scopeof the claims.

I claim:

1. The combination of a paraffin scraper with a sucker rod wherein saidscraper comprises a substantially cylindrical body having a longitudinalbore therethrough to receive the rod and having a longitudinal slotthrough the body and communicating with said bore, the diameter of thesucker rod being smaller than the diameter of the bore and greater thanthe width of the slot; a plurality of scraping blades symmetricallydisposed around the outer periphery of the body and standing outwardlytherefrom, the blades each being disposed at an inclined angle withrespect to the longitudinal bore and each having an outer bearingsurface forming part of a cylinder coaxial with respect to the bore, thesides of the blades being disposed substantially normal to the outersurface of the body, and the body having a plurality of grooves recessedinto its inner peripheral surface Within the bore and providing scrapingedges therein.

2. A one-piece molded paraflin scraper consisting entirely of plasticand comprising a substantially cylindrical body having an axiallydisposed longitudinal bore therethrough and having a slot through thebody communicating with said bore, the Wi th of the slot being less thanthe diameter of the bore; a plurality of scraping blades symmetricallydisposed around the outer periphery of the body and standing outwardlytherefrom, the blades each being disposed at an inclined angle withrespect to the longitudinal bore and each having an outer bearingsurface forming part of a cylinder coaxial with respect to the bore, andthe sides of the blades being disposed substantially normal to the outersurface of the body; the body having a plurality of grooves recessedinto its inner peripheral surface within the bore and providing scrapingedges therein.

3. In a scraper as set forth in claim 2, said plastic comprising nylon.

References Cited in the file of this patent UNITED STATES PATENTS1,605,316 Wilson Nov. 2, 1926 1,677,050 Reed et al. July 10, 19281,810,260 Swinford June 16, 1931 2,295,058 Smethers Sept. 8, 19422,715,552 Lane Aug. 16, 1955 2,793,917 Ward May 28, 1957 2,928,472Tripplehorn May 15, 1960

